Airbag and an airbag fabric comprising a polyamide yarn

ABSTRACT

An object of the present invention is to provide an airbag module ensuring that when an airbag fabricated using a fabric composed of a polyamide yarn excellent in heat resistance is deployed by an inflator gas, the deployment occurs without loss of the gas and an excessive amount of generated gas is not necessary, as a result, the inflator is reduced in weight, and the airbag module of the present invention comprises an airbag fabric composed of a polyamide yarn, wherein the air permeability of the fabric under a pressure of 200 kPa is from 10 to 200 cc/cm 2 /sec and in the thermal stress of the constituent yarn as measured under the conditions of an initial load of 0.02 cN/dtex, a yarn length of 25 cm and a temperature rise rate of 80° C./min, the summed thermal stress of the total of the warp yarn and the weft yarn at 230° C. is from 0.33 to 1.20 cN/dtex.

This is a division of application Ser. No. 13/390,482, §371(c) date ofFeb. 14, 2012, pending, which claims the benefit of PCT/JP2010/059383,filed Jun. 2, 2010, and claims benefit to JP 2009-256424, filed Nov. 9,2009, all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an airbag capable of absorbing impacton the human body in a vehicle accident and protecting the human body.More specifically, the present invention relates to an airbag fabric, anairbag and an airbag module, which are lightweight and has excellentstorability.

BACKGROUND ART

In order to relieve impact on the human body in a car accident, mountingof an airbag in a vehicle is proceeding. As an airbag capable ofinflating by gas or the like and absorbing impact on the human body in acollision, for the protection of an occupant, a curtain airbag, a sideairbag, a knee airbag, a rear airbag and the like are being put intopractice, in addition to a driver's sheet airbag and a passenger sheetairbag. Furthermore, for the protection of a pedestrian, mounting ofvarious airbags such as an airbag on the outside of the vehicle is indiscussion. On the other hand, with the growing interest inenvironmental problems, from the standpoint of improving fuel efficiencyof a vehicle, weight saving is also required of an airbag module. Also,in order to enhance fuel efficiency or energy efficiency by reducingvehicle size, the region in which the airbag module is stored isbecoming narrower, and more reduced size is necessary.

The airbag module mainly comprises an airbag obtained by forming afabric composed of a synthetic fiber into a bag shape, an inflator forgenerating gas capable of deploying the airbag, and a device fordetecting a collision and controlling the deployment. Of these members,the inflator is composed of a strong container for housing a propellantin the container and generating a high-pressure high-speed gastherefrom, or composed of a strong high-pressure gas container forhousing a high-pressure gas in the container and generating ahigh-pressure high-speed gas by opening the container with an explosive.Accordingly, its weight or volume accounts for a large part of theairbag module.

As for the airbag, in order to reduce the weight thereof, reducing thefineness of the fiber constituting the airbag fabric or fabrication of anon-coated airbag by using an airbag fabric substantially uncoated witha resin or an elastomer is being carried out.

Compared with a coated airbag, the deployment gas in the non-coatedairbag is not sufficiently utilized. In an airbag for front collisionaccident, such as a driver's seat airbag and passenger seat airbaghaving a long history of airbag mounting, after the airbag is deployedby gas, the gas is released from a vent hole provided in the airbag or afilter fabric part so as to receive the human body and thereby theimpact energy is absorbed. Accordingly, the amount of leakage of thedeployment gas in the non-coated airbag is not strictly taken as aproblem. However, in recent years, a change in the deployment size ofthe airbag by controlling the opening of the vent hole or employing anairbag undergoing stepwise the deployment is proceeding. Further,mounting a side curtain airbag aimed at quick deployment without thevent hole is being employed. In turn, also as the non-coated airbag, anairbag ensuring more reduction in the loss of the deployment gas duringdeployment than ever is demanded. Furthermore, when there is no loss ofthe deployment gas, the volume of the inflator need not be excessivelyincreased and the airbag module can be expected to be reduced in thesize.

With respect to the air permeability of the non-coated airbag under highpressure, Patent Document 1 discloses a technique demonstrating thathigher air permeability is more effective in reducing the impart, butthe desire is to increase the gas utilization efficiency by suppressingthe air permeability under high pressure as much as possible. Also,Patent Document 2 discloses an airbag technique of fabricating anon-coated airbag by using a fabric composed of a polyester filamentyarn to cause no change in the permeability or bursting strength under ahigh-temperature high-humidity environment, but in a polyester fabric, amelted hole may be produced due to burning residue from the propellantin the inflator and a rupture may be caused, and it is demanded tofabricate an airbag fabric ensuring lower air permeability under highpressure by using a polyamide fabric excellent in heat resistance.

With respect to the pressure resistance of the airbag after a heattreatment, Patent Document 3 describes excellent tear tenacity retentionof a polycapramide fiber after a heat treatment, but for preventing theairbag from melting and rupturing due to a high-temperature gas orreaction residue in case of using an explosive for the inflation gas,the fiber above is inferior to the polyamide 6•6 fiber in view ofmelting temperature. In the fabric composed of a polycapramide fiber,bag deployment by an explosive is improper. Patent Document 4 describesa technique of enhancing the tear tenacity by imparting apolysiloxane-based softener by immersion, but it is unprofitable tospecially use a treating agent or increase the processing step. Also,the weaving yarn in the sewn part is slid off to cause fiber dropout,and this impairs the strength of the sewn part. Patent Document 5demonstrates that in the finish oil-imparted fabric without scouring,the tear tenacity may be maintained, but this document is silent aboutthe characteristics such that the deployment speed is maintained after aheat treatment. Patent Document 6 demonstrates that by incorporating athermal stabilizer into a polycapramide fiber to make an original yarnallowing generation of a thermal shrinkage stress at a highertemperature, the increase in air permeability of the airbag base clothafter a heat treatment can be suppressed. However, even if low airpermeability is maintained after a heat treatment, characteristicsnecessary to maintain the deployment speed are not described.

Conventionally, for the airbag mounted in the interior of an automobile,i.e., in a cabin, it is important that the airbag stored for a long termunder the conditions of summer and daytime high temperatures or winterand nighttime low temperatures maintains the deployment performance suchas pressure resistance at the actuation of inflation and deploymentafter the elapse of days. However, the place in which an airbag loadedto inflate toward the outside of the vehicle for the protection of apedestrian is mainly mounted is outside the cabin and particularly, whenthe place is near the engine room inside the bonnet, the airbag isexposed to a harsher environmental condition. That is, durability of theairbag under a harsh environment is more stringently required. The taskis to maintain the deployment performance after the elapse of days underharsher environmental conditions.

The airbag for the protection of a pedestrian takes such a large areaand a large dimension as covering the front part of the bonnet or thelower part of the front glass. Also, compared with the case of relievingthe short distance collision in an automobile, large inflation is used.Accordingly, such an airbag is a large-volume airbag, but the deploymentspeed of the airbag stored for a long term is disadvantageously slowedafter many days. Even when a proper deployment timing of the airbag isadjusted by a detector or a deployment/ignition control device, if thetiming is lagged because of, for example, a delay caused until the gasfunctions by permeating from end to end during deployment of the bag,the impact absorbing performance is deteriorated. Accordingly, the taskis also to maintain the deployment speed of a large-volume airbag underharsh environmental condition.

PRIOR ART Patent Document

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2002-317343-   Patent Document 2: Japanese Unexamined Patent Publication No.    6-306731-   Patent Document 3: Japanese Unexamined Patent Publication No.    10-60750-   Patent Document 4: Japanese Unexamined Patent Publication No.    8-41751-   Patent Document 5: Japanese Unexamined Patent Publication No.    5-339840-   Patent Document 6: Japanese Unexamined Patent Publication No.    2006-183205

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide an airbag moduleensuring that when an airbag fabricated using a fabric composed of apolyamide fiber excellent in heat resistance is deployed by an inflatorgas, the deployment is performed without loss of the gas and anexcessive amount of generated gas is not required, as a result, theinflator is reduced in the weight. In particular, an object of thepresent invention is to provide an airbag module where a non-coatedairbag is excellent in the burst resistance and capable of performinghigh-speed deployment without loss of gas. Another object of the presentinvention is to provide an airbag module having high reliability evenunder a high-temperature high-humidity environment.

Means to Solve the Problems

In order to attain the above-described objects, the present inventionhas the following configurations.

(1) An airbag fabric comprising a polyamide yarn, wherein the airpermeability of the fabric under a pressure of 200 kPa is from 10 to 200cc/cm²/sec and in the thermal stress of the constituent yarn as measuredunder the conditions of an initial load of 0.02 cN/dtex, a yarn lengthof 25 cm and a temperature rise rate of 80° C./min, the summed thermalstress of the total of the warp yarn and the weft yarn at 230° C. isfrom 0.33 to 1.20 cN/dtex.

(2) The airbag fabric as described in item 1 above, wherein from 0.1 to100 ppm in total of at least one element selected from zinc, aluminumand magnesium, from 10 to 500 ppm of a copper element, from 100 to 3,500ppm in total of iodine and/or bromine, and from 0.01 to 20 ppm of aniron element are contained in the fabric.

(3) The airbag fabric as described in item 2 above, which comprises apolyamide fiber melt-spun with the addition of a fatty acid metal salt.

(4) The airbag fabric as described in any one of items 1 to 3 above,wherein the cyclic unimer content in the fabric is from 0.1 to 3.0%based on all amide bond units.

(5) The airbag fabric as described in item 4 above, wherein thepolyamide fiber is obtained by melt-spinning with the addition of anoligomer containing a cyclic unimer.

(6) The airbag fabric as described in any one of items 1 to 5 above,wherein the content of the finish oil component in the fabric is from0.01 to 2.0 wt %.

(7) The airbag fabric as described in any one of items 1 to 6 above,wherein the total widening Ws as the sum of the widening ratio R(f) ofthe weft yarn and the widening ratio R(w) of the warp yarn on the fabricsurface is from 0 to 40%.

(8) The airbag fabric as described in any one of items 1 to 7 above,wherein the widening ratio R(f) of the weft yarn on the fabric surfaceis from 90 to 120% and the widening ratio R(w) of the warp yarn on thefabric surface is from 105 to 135%.

(9) The airbag fabric as described in any one of items 1 to 8 above,wherein in the stress-strain curve of the fabric, the total value of theelongation under a load corresponding to 4.0 cN/dtex in terms of astress per one yarn constituting the fabric in the warp direction andthat in the weft direction is from 40.0 to 58.0%.

(10) The airbag fabric as described in any one of items 1 to 9 above,wherein in DSC measurement of measuring the fabric at a temperature riserate of 20° C./min, the melting initiation temperature is from 245 to280° C. and the heat of melting is from 60 to 100 J/g.

(11) The airbag fabric as described in any one of items 1 to 10 above,wherein the thermal stress determined by measuring the constituent yarnof the fabric under the conditions of an initial load of 0.02 cN/dtex, ayarn length of 25 cm and a temperature rise rate of 80° C./min is from0.005 to 0.10 cN/dtex at 120° C. in both the warp yarn and the weftyarn.

(12) The airbag fabric as described in any one of items 1 to 11 above,wherein the constituent yarn is a polyamide 6•6 yarn having a relativeviscosity of 2.7 to 4.7, a single filament fineness of 0.8 to 8.0 dtex,a total yarn fineness of 100 to 800 dtex, a tensile tenacity of 5.0 to11.0 cN/dtex, an elongation at break of 15 to 35% and a shrinkage inboiling water of −4.5 to 5.0%.

(13) The airbag fabric as described in any one of items 1 to 12 above,which is not coated with a resin or an elastomer.

(14) An airbag using the airbag fabric described in any one of items 1to 13 above.

(15) An airbag module using the airbag described in item 14 above.

Effects of the Invention

The airbag fabric of the present invention is composed of a polyamidefiber excellent in heat resistance and despite excellent storability,capable of restraining the passage of deployment gas during deploymentby a high-temperature gas and furthermore, reducing the gas leakage fromthe sewn part after thermal aging, and can fabricate an airbag overallexcellent in utilization of the deployment gas. Accordingly, the entireamount of the gas produced in the inflator can be made use of andutilized for deployment, so that a lightweight small airbag module canbe provided without excessively increasing the volume of the inflatorused for the airbag module. Also, due to the strengthened sewn part, theburst resistance is excellent and high-speed deployment becomespossible. Furthermore, the physical properties are restrained fromchanging with thermal aging and an airbag module having high reliabilityeven under a high-temperature high-humidity environment can be provided.

MODE FOR CARRYING OUT THE INVENTION

The present invention is specifically described below.

The polyamide fiber constituting the fabric of the present inventionincludes a fiber composed of polyamide 6, polyamide 6•6, polyamide 11,polyamide 12, polyamide 6•10, polyamide 6•12, polyamide 4•6, a copolymerthereof, and a mixture thereof. In particular, a polyamide 6•6 fiber ispreferred, and the polyamide 6•6 fiber is preferably composed of mainlya polyhexamethylene adipamide fiber. The polyhexamethylene adipamidefiber indicates a polyamide fiber consisting of 100% ofhexamethylenediamine and adipic acid and having a melting point of 250°C. or more. The polyamide 6•6 fiber for use in the present invention maybe a fiber composed of a polymer obtained by copolymerizing or blendingpolyamide 6, polyamide 6•I, polyamide 6•10, polyamide 6•T or the likewith polyhexamethylene adipamide within the range keeping the meltingpoint from becoming less than 250° C.

The relative viscosity ηr of the polyamide 6•6 fiber is preferably from2.7 to 4.7. When the relative viscosity ηr is 2.7 or more, the fabricconstituent yarn can be a high-strength yarn contributing to thestrength-elongation characteristics good enough as an airbag fabric.Also, when the relative viscosity is 4.7 or less, mixing of a weak yarnand a thin yarn is eliminated, and a high-quality fabric as an airbagfabric is easily obtained without suffering an adverse effect ofproducing a conspicuous fabric defect due to broken filaments in yarn.The relative viscosity ηr as used herein is determined by dissolving 2.5g of a sample in 25 cc of concentrated sulfuric acid (98%) and measuringthe solution by an Ostwald viscometer at a given temperature in aconstant-temperature bath (25° C.).

The polyamide 6•6 polymer is synthesized through condensationpolymerization by solution polymerization and includes a polymer bycontinuous polymerization and a polymer by batch polymerization. In thepresent invention, for adjusting the relative viscosity ηr to from 2.7to 4.7, the polymerization degree is increased by further subjecting thepolymer by the process of both polymerizations to removal ofcondensation water in a solid-phase polymerization step. Further, thepolymerization degree is increased by providing a vacuum step as thefinal step of the continuous polymerization process and removing thecondensation water, whereby a high-viscosity polymer can be obtained.

The polyamide 6•6 polymer is spun into a polyamide 6•6 fiber by a meltextruder. The polymer may be also spun directly after the continuouspolymerization process. In the course of melt extrusion, the moisturepercentage in the polymer is controlled, whereby the relative viscosityηr of the polyamide 6•6 fiber constituting the fabric of the presentinvention can be controlled. In particular, high ηr is obtained by a lowmoisture percentage. The moisture percentage in the polymer can becontrolled by applying drying or moisture absorption to the polymerbefore melting or by vacuum suctioning the polymer during melting.

The shrinkage in boiling water of the polyamide 6•6 fiber constitutingthe fabric is 5.0% or less, and as the shrinkage is lower, the fabrichas higher shape stability and in the case of a large airbag, the shapecan be prevented from changing with aging in a high-temperatureenvironment. Also, the tear resistance in a harsh environment, i.e.,after thermal aging, is good and this contributes to enhancing the gaspressure resistance of the airbag. Furthermore, change in the airpermeability is suppressed and due to the crimp morphology of the fiber,the fabric exhibits good flexibility, so that a short deployment time ofthe airbag can be maintained. The shrinkage in boiling water of thepolyamide 6•6 yarn constituting the fabric is derived from the shrinkagein boiling water of the original polyamide 6•6 fiber as the weavingyarn, and is determined in the course of drying and heatsetting thefabric. The shrinkage in boiling water of the original polyamide 6•6fiber as the weaving yarn is preferably 10.0% or less, more preferably8.0% or less. Furthermore, by controlling the temperature, residencetime and tension so that shrinkage is developed in the course of dryingand heatsetting the fabric, the shrinkage in boiling water of thepolyamide 6•6 yarn constituting the fabric can be kept to a lowshrinkage of 5.0% or less. As the shrinkage in boiling water of thepolyamide 6•6 yarn constituting the fabric, both full shrinkage andapparent minus shrinkage due to water absorption by a boiling watertreatment, that is, shrinkage in which elongation is observed, are alsopreferred. Accordingly, the shrinkage in boiling water of the polyamide6•6 yarn constituting the fabric is preferably −4.5% or more. Theshrinkage in boiling water is preferably from −4.5 to 5.0%, morepreferably −4.0 to 3.0%, still more preferably from −3.0 to 2.5%.

The single filament fineness and total yarn fineness of the polyamide6•6 yarn greatly affect mechanical characteristics and storability as anairbag and therefore, the single filament fineness is preferably from0.8 to 8.0 dtex, more preferably from 1 to 7 dtex. When the singlefilament fineness is 0.8 dtex or more, a fiber defect or the likederived from single filament breaking, for example, in the weaving stepcan be avoided. The single filament fineness is 8.0 dtex or less and asthis fineness is smaller, a fabric ensuring lower bulkiness of thefolded fabric and better airbag storability is provided.

The total yarn fineness is preferably from 100 to 800 dtex, morepreferably from 200 to 500 dtex. When the total yarn fineness is 100dtex or more and as thicker, the tenacity of the airbag fabric becomeshigher and the gas pressure resistance of the airbag is increased. Whenthe total yarn fineness is 800 dtex or less and as thinner, alightweight fabric results. It is better to appropriately match thesingle filament fineness or the total yarn fineness in the above ranges.

The tensile tenacity of the polyamide 6•6 yarn constituting the fabricis preferably from 5.0 to 11.0 cN/dtex, more preferably from 6.0 to 10.5cN/dtex, and most preferably from 7.0 to 10.0 cN/dtex. The elongation atbreak is preferably from 15 to 35%.

When the tensile strength is as high as 5.0 cN/dtex or more, thetenacity as an airbag fabric is excellent. The polyamide 6•6 yarn havinga tensile strength of 11.0 cN/dtex or less is balanced between thetensile strength and the elongation at break. Also, when the elongationat break is 15% or more, the fabric is kept from becoming coarse andhard, whereas the polyamide 6•6 yarn having an elongation at break of35% or less is balanced between the elongation at break and the tensilestrength. The tensile strength of the polyamide 6•6 yarn constitutingthe fabric is mainly derived from the tensile strength of the originalpolyamide 6•6 fiber used as the weaving yarn. The tensile strength ofthe polyamide 6•6 fiber as the weaving yarn is preferably about 5.5cN/dtex or more, and the fabric can be composed of a high-strength yarnfree from abnormal abrasion even in a high-density weaving process. Theelongation at break of the polyamide 6•6 yarn constituting the fabric ismainly derived from the elongation at break of the polyamide 6•6 fiberused as the weaving yarn. The elongation at break of the polyamide 6•6fiber as the weaving yarn is preferably about 20.0% or more and in thiscase, the fabric can be composed of a high-elongation yarn free fromabnormal tension load even in a high-density weaving process.

In DSC measurement of measuring the fabric at a temperature rise rate of20° C./min, the fabric of the present invention preferably has a meltinginitiation temperature of 245 to 280° C. and a heat of melting of 60 to100 J/g. For comparing the meltability in the state of the airbag beinggas-inflated, the fabric sample is measured by placing a fabric ofalmost the same size as the pan for DSC measurement on the bottom of thepan, and fixing the outer peripheral end of the sample by swagingtogether with the pan cover, thereby confining the sample. The meltinginitiation temperature is a temperature at which in advance of crystalmelting, the polymer orientation in the lower temperature fiber startsundergoing entropic relaxation. When the melting initiation temperatureis 245° C. or more and the heat of melting is 60 J/g or more, flyingcoming of a residue, i.e., a hot particle, produced by the deploymentgas generation in the inflator is less liable to produce a melted holein the fabric and lead to rupture or bursting. The heat of melting isderived from the crystal melting of the polyamide polymer. When theenthalpy of crystal melting is high and crystallization degree is high,the heat of melting is large, but the enthalpy of crystal melting isdetermined by the difference in the enthalpy between the crystal stateand the melted state and therefore, the heat of melting isthermodynamically determined by selecting the polyamide polymer chain.The crystallization degree varies depending on the heat treatmentconditions when spinning and stretching the polymer, and ahigh-temperature hot stretching is effective. However, the polyamidefiber is a paracrystal where a fine crystal is mixed with an amorphouspart, and is limited in the crystallization degree. As a result, inpractice, the heat of melting is 100 J/g or less. The heat of melting ismore preferably from 70 to 90 J/g.

The melting initiation temperature is a temperature at which highorientation of the polymer chain starts being relaxed, and is affectedby the polymer structure fixing resulting from hot drawing in thespin-draw step, the heat setting of the polymer structure in theweaving/processing step, or the cloth structure. The melting initiationtemperature precedes crystal melting and is at the highest a crystalmelting temperature of the polyamide fiber and 280° C. or less. Themelting initiation temperature is more preferably from 248 to 270° C.For raising the melting initiation temperature, the orientation of thepolyamide yarn constituting the fabric is preferably heat-set, and theshrinkage in boiling water of the yarn constituting the fabric ispreferably 5.0% or less and not lower than −4.5%, more preferably notlower than −4.0%, still more preferably 4.0% or less and not lower than−3.0%. The melting initiation temperature is higher as the yarn woven ata high density are more tightly bound to each other and therefore, thecover factor of the fabric is preferably 2,000 or more, more preferably2,200 or more, still more preferably 2,300 or more. The cover factor asused herein is a value obtained by adding the product of the square rootof fineness (dtex) and the weave density (yarns/2.54 cm) of the warpyarn to that of the weft yarn.

In the fabric of the present invention, the air permeability under apressure of 200 kPa at ordinary temperature is preferably from 10 to 200cc/cm²/sec. When the air permeability at ordinary temperature is 200cc/cm²/sec or less and as lower, the gas leakage during deployment by ahigh-temperature gas is reduced. In order to reduce the air permeabilityunder a pressure of 200 kPa at ordinary temperature, the cover factor ofthe fabric is preferably 2,000 or more, more preferably 2,200 or more,still more preferably 2,300 or more. Also, the single filament finenessof the fiber constituting the fabric is preferably from 0.8 to 8.0 dtex,more preferably from 1.0 to 7.0 dtex, and as the fineness is thinner,the air permeability can be more reduced. The single filament finenessis still more preferably from 1.5 to 5.0 dtex. Keeping low the airpermeability under high pressure at ordinary temperature is a necessaryrequirement for the low air permeability during deployment by ahigh-temperature gas. The gas is preferably blocked to such an extent asnot being observed, but in view of balance with other characteristics,the lower limit of the air permeability is 10 cc/cm²/sec. The airpermeability under a pressure of 200 kPa at ordinary temperature is morepreferably from 20 to 180 cc/cm²/sec, still more preferably from 50 to180 cc/cm²/sec.

In the weaving yarn on the surface of the fabric of the presentinvention, with respect to the maximum width W (mm) of an area wherewarp and weft yarns are woven and filaments of the weaving yarn arealigned, it is preferred that the widening ratio R(f) of the weft yarnis from 90 to 120%, the widening ratio W(w) of the warp yarn is from 105to 135%, and the total widening Ws is from 0 to 40%.Widening ratio R(f)={W(f)/(25.4/D(f))}×100Widening ratio R(w)={W(w)/(25.4/D(w))}×100Total widening Ws=R(f)+R(w)−200.

In the above, W(f) is the maximum width (mm) of the weft yarn, W(w) isthe maximum width (mm) of the warp yarn, D(f) is the weave density(yarns/25.4 mm) in the weft direction, and D(w) is the weave density(yarns/25.4 mm) in the warp direction.

The widening ratio is the percentage of the maximum weaving yarn widthobserved on the fabric surface, based on the weaving yarn pitchcalculated from the weave density. The total widening is obtained bytotalizing the widening ratios in the warp and weft directions andindicates the inflation beyond the weaving yarn pitch. When the totalwidening Ws is 0 or more, for the entire fabric, widening of the weavingyarn leads to overlapping of fibers blocking the passing of gas and theair permeability can be reduced. As both the total widening Ws and thewidening ratio R are larger, the air permeability are more reduced.Also, when the total widening Ws is 40% or less, there is no fear thatthe filaments other than the widened filaments sag and the airpermeability under high pressure is rather increased. The total wideningWs is preferably from 2 to 30%. When the widening ratio R(w) of the warpyarn is 105% or more, the warp yarns are unfailingly overlapped witheach other and the passing of air is blocked. When the widening ratioR(w) of the warp yarn is 135% or less, there is no fear that thefilaments other than the widened filaments sag and the air permeabilityunder high pressure is rather increased. The widening ratio R(w) of thewarp yarn is more preferably from 110 to 130%. When the widening ratioR(f) of the weft yarn is 90% or more, low air permeability results. Whenthe widening ratio R(f) of the weft yarn is 120% or less, there is nofear that the filaments other than the widened filaments sag and the airpermeability under high pressure is rather increased. The widening ratioR(f) of the weft yarn is more preferably from 93 to 110%. Due to theweaving yarn configuration where the weaving yarns on the fabric surfaceare overlapped and the above-described widening ratio and total wideningare satisfied, the air permeability can be reduced and the airpermeability under high pressure of the fabric can be made low.

The widening ratio or total widening may be increased by increasing theweave density by the fabric design, and furthermore, appropriatelyapplying shrinking processing after weaving to increase the warp-weftweave density in a balanced manner. In the case of using a twisted yarnfor the weaving yarn in the weaving step, a high-density fabric isliable to be woven due to gathering and bundling particularly of singlefilament in warp yarns, but good bundling of filaments on the fabricsurface reduces the widening ratio or the total widening. Accordingly,it is preferred that the weaving yarn in the fabric is substantially nottwisted. That is, slight loose twisting caused when taking out the yarnfrom a package is usually present in the weaving yarn at a frequency ofless than 10 twists/m, but the weaving yarn is preferably used withoutapplying any more intentional twisting. Furthermore, when airentanglements are applied to the weaving yarn in the yarn-making step orthe like, the single filament can be prevented from breaking due todisentangle of filaments during handing of the weaving yarn, but goodbundling of filaments on the fabric surface reduces the widening ratioor total widening. Accordingly, it is preferred that the entanglementsare substantially eliminated when the yarn is processed into a fabric.In the raveled yarn from the fabric, no entanglements are preferablyobserved by the water surface observation method. Accordingly, theentanglements of the weaving yarn original yarn used for the fabric arepreferably from 1 to 15 entanglements/m, more preferably from 1 to 10entanglements/m.

In the tensile test of the fabric of the present invention, the totalvalue of such elongation in the warp direction as letting the load perone yarn constituting the fabric become 4.0 cN/dtex (hereinafter,referred to as a specific load-elongation) and that in the weftdirection is preferably from 40.0 to 58.0%. When the total of thespecific load-elongation in the tensile test of the fabric is 58.0% orless and as smaller, air permeability of the fabric when an expansionstress is imposed by gas is more successfully kept low. The total of thespecific load-elongation is more preferably from 45.0 to 54.0%, stillmore preferably from 51.0% or less. For reducing the total of thespecific load-elongation in the tensile test of the fabric, theelongation under a load of 4.0 cN/dtex in the tensile test of theoriginal yarn fiber constituting the weaving yarn for both the warp andweft yarns is preferably small and 15% or less. The elongation is morepreferably 13% or less. Furthermore, in the heatsetting after theweaving of the fabric, the fabric may be cooled and fixed byappropriately keeping a strain in each of the warp and weft direction.When the total of the specific load elongation in the tensile test ofthe fabric is 40.0% or more, the fabric does not become coarse and hard.In the original yarn fiber constituting the fabric, the elongation undera load of 4.0 cN/dtex in the tensile test is preferably 5% or more, morepreferably 7% or more.

In the present invention, the thermal stress determined by measuring thefiber constituting the fabric under the conditions of an initial load of0.02 cN/dtex, a sample length of 25 cm and a temperature rise rate of80° C./min is preferably from 0.005 to 0.10 cN/dtex at 120° C. in boththe warp yarn and the weft yarn. Also, in the thermal stress at 230° C.measured under the same conditions, the summed thermal stress of thetotal of the warp yarn and the weft yarn is preferably from 0.33 to 1.20cN/dtex. When the thermal stress at 120° C. is 0.10 cN/dtex or less andis low, the fabric during storage of the airbag exhibits gooddimensional stability in a high-temperature environment. The thermalstress is more preferably 0.05 cN/dtex or less. Due to such thermalstress, the air permeability in the sewn part is kept from increasingdue to generation of wrinkling in the sewn part. The thermal stress at120° C. for being thermally stable is substantially 0.005 cN/dtex ormore. When the summed thermal stress at 230° C. is as high as 0.33cN/dtex, the air permeability of the fabric upon generation of anexpansion stress at a high temperature during deployment of the airbagcan be kept low. In turn, gas leakage during deployment by ahigh-temperature gas is reduced. When the summed thermal stress at 230°C. is 1.2 cN/dtex or less, there is no fear that the thermal stress at120° C. becomes excessively high. The summed thermal stress at 230° C.is more preferably from 0.35 to 1.00 cN/dtex.

The thermal stress at 120° C. can be reduced by selecting thehigh-temperature stretching conditions for the stretching conditions ofthe polyamide yarn. The thermal stress can be also reduced by selectingproper shrinkage in the scouring and heatsetting after the weaving ofthe fabric. For example, in the case of a weaving original yarn having ahigh shrinkage percentage, the thermal stress can be reduced mainly bythermal shrinkage in the high-temperature scouring or the like, but thisinvolves reduction in the entire thermal stress including the thermalstress at a high temperature of 230° C. and therefore, the shrinkageconditions must be balanced. Also, in the case of a weaving originalyarn having a low shrinkage percentage, the thermal stress at a lowtemperature is small and shrinkage in a scouring step or the like may beomitted, but on the other had, there is a fear that the thermal stressat a high temperature becomes excessively small.

The thermal stress at 230° C. can be reduced by selecting the coolingconditions after thermal stretching for the stretching conditions of thepolyamide yarn. That is, the yarn-making may be performed by stepwisedecreasing the processing temperature condition to about 150° C. fromthe thermal drawing temperature and in the course of this temperaturedrop, stepwise reducing the thermal tension at an elongation/relaxationrate. The conditions of scouring after the weaving of the fabric shouldbe appropriately selected so as not to significantly impair the thermalstress, and it is rather preferred to perform no scouring. Also, thesubsequent heatsetting of the fabric may be performed at a temperatureof preferably from 120 to 200° C. while keeping the strain withoutrelieving the tension, and immediately after the heat treatment, thefabric may be cooled while appropriately keeping the strain in each ofthe warp and weft directions of the fabric without relieving thetension.

In the yarn constituting the fabric of the present invention, theinitial rigidity, that is, the stress, at an elongation of 2.5% in thetensile test is preferably from 0.10 to 1.00 cN/dtex. When the initialtensile modulus is as small as 1.00 cN/dtex or less, the fabric isinsusceptible to a folding habit (pleat) and liable to be avoided fromhaving a trigger to rupture of the airbag. For keeping the initialtensile modulus of the yarn constituting the fabric small, a fibercomposed of an aliphatic polyamide resin, which is a fiber by a directspinning and drawing method, is used. Furthermore, in the textileprocessing, it is preferred to avoid applying a strain under suchconditions as allowing development of shrinkage in the scouring orheatsetting or not to perform scouring or heatsetting.

The fabric of the present invention preferably contains from 10 to 500ppm of a copper element and also preferably contains from 100 to 3,500ppm in total of iodine and/or bromine elements. These are contained as athermal stabilizer for the polymer molecule of the polyamide to enhancethe long-term heat resistance. The content of the copper element is morepreferably from 15 to 300 ppm, more preferably from 20 to 200 ppm, andmost preferably from 30 to 100 ppm. The content in total of the iodineand/or bromine elements is more preferably from 150 to 3,000 ppm, morepreferably from 200 to 2,500 ppm, and most preferably from 250 to 2,000ppm. The copper element exerts an action of scavenging a radicaloriginated from cleavage of the molecular chain of the polyamidepolymer. When the copper element is 10 ppm or more and as larger, thelong-term heat resistance of the polyamide polymer can be expected to beenhanced. Accordingly, the airbag after thermal aging can be avoidedfrom bursting or rupture at the deployment by gas. When the copperelement is 500 ppm or less, this is profitable, and a trouble such asaccumulation of an inorganic deposit in the spinning step is hardlycaused. The iodine and/or bromine elements are used to let the copperrepeatedly develop its radical scavenging action and thereby maintainthe thermal stabilization effect by the copper.

The copper element is added as a copper compound to the polyamidepolymer. Specific examples of the copper compound include cuprouschloride, cupric chloride, cupric bromide, cuprous iodide, cupriciodide, cupric sulfate, cupric nitrate, copper phosphate, cuprousacetate, cupric acetate, cupric salicylate, cupric stearate, cupricbenzoate, and a complex compound of the inorganic copper halide abovewith xylylenediamine, 2-mercaptobenzimidazole or benzimidazole. Inparticular, addition of a monovalent copper halide compound composed ofa combination of a copper compound and a halogen is more preferred, andspecific preferred examples of the compound added include cuprousacetate and cuprous iodide.

The iodine and/or boron elements can be added as an alkali halidecompound. Examples of the alkali halide compound include lithiumbromide, lithium iodide, potassium bromide, potassium iodide, sodiumbromide and sodium iodide. The iodine and/or bromine elements are addedto regenerate the function of the copper by an oxidation-reductionreaction when the copper contributes to radical scavenging, and thecontent of these elements is preferably 100 ppm or more, more preferably300 ppm or more. As the content is larger, the long-term heat resistanceof the polyamide polymer can be expected to be enhanced. On the otherhand, when the content is 3,500 ppm or less, yellowing due to liberationof iodine in a general environment can be avoided.

The content of the iron element contained in the fabric of the presentinvention is preferably from 0.01 to 20 ppm, more preferably from 0.05to 10 ppm, still more preferably from 0.1 to 5 ppm. When the content ofthe iron element is 20 ppm or less and as smaller, the polyamide andpolyamide oligomer component are limited from oxidative decomposition,and holding the heat resistance by the copper and the halogen compoundcan be more effectively enjoyed. Then, Oxidative decomposition of thepolyamide after thermal aging is limited, and reduction in themechanical properties is suppressed. In turn, the airbag base clothsubject to an increasing load when performing the deployment in a highlyairtight manner after thermal aging is not ruptured, and the reliabilitycan be more enhanced. The iron element is incorporated into thepolyamide polymer in the spinning and filtration step where out of thepolymerization and spinning step, the temperature is highest and themetal contact area is large. An alloy material having a small ironcontent, such as nickel alloy (e.g., Hastelloy (trademark)), ispreferably employed for the metal nonwoven fabric used in a spinningfilter. The content of the iron element in the polyamide yarn isindustrially 0.01 ppm or more.

The fabric of the present invention preferably contains from 0.1 to 100ppm in total of any one or all of zinc, aluminum and magnesium elements.The content of these elements is more preferably from 0.5 to 50 ppm,still more preferably from 1.0 to 30 ppm, and most preferably from 5.0to 20 ppm. When the fabric contains 0.1 ppm or more in total of zinc,aluminum and magnesium elements, even in a high-temperature environmentor a high-humidity environment, the fabric composed of the polyamidefiber can be kept from reduction in the physical properties due todeterioration of the polyamide fiber. When the total content of zinc,aluminum and magnesium elements in the polyamide yarn is 100 ppm orless, a spinning failure due to addition of an additive containing theelement above to the polyamide yarn, that is, a fabric defect of thepolyamide yarn fabric due to yarn breaking or single filament breaking,can be avoided. Furthermore, the total amount of zinc, aluminum andmagnesium elements preferably exceeds the amount of the iron element.Also, out of three elements, the content of the aluminum element ispreferably the principal amount and accounts for 40% or more, morepreferably 60% or more.

In the fabric of the present invention, the zinc, aluminum and magnesiumelements contained in the polyamide yarn are preferably incorporated byspinning yarns with the addition of a fatty acid metal salt to thepolyamide polymer. The fatty acid metal salt added to the polyamidepolymer is preferably a metal salt of a fatty acid having a carbonnumber of 6 to 40, and specific examples thereof include aluminummontanate, magnesium montanate, zinc montanate, aluminum stearate,magnesium stearate, and zinc stearate. Among these, aluminum montanate,magnesium montanate and zinc montanate can be preferably used. Such afatty acid metal salt has little action for thermal deterioration of thepolyamide polymer, facilitates obtaining a high-strength fiber due toits nucleating effect, contributes to enhancement of seam tenacity ofthe fabric resulting from improved uniformity of physical properties ofthe fiber, and particularly contributes to enhancement of seam tenacityof the fabric after thermal aging. In turn, the thermally aged airbagcan be prevented from bursting. In the present invention, one kind ofthe above-described aliphatic metal salt may be used, or two or morethereof may be used in combination.

In the fabric of the present invention, the polyamide oligomer ispreferably controlled to an appropriate content. For this purpose, it ispreferred to appropriately control the polyamide oligomer content duringspinning into a polyamide fiber. In particular, the fabric preferablycontains a cyclic unimer where a hexamethylenediamine and an adipic acidare circularly condensed one by one, in an amount of 0.1 to 3.0%, morepreferably from 0.5 to 2.5%, based on all amide bond units. The cyclicunimer as used herein is a compound represented by the following formula(1):

Among polyamide oligomers, the cyclic unimer has a low molecular weightand is cyclic, which are effective for slowly bleeding out to the fibersurface while keeping the plasticization effect. Furthermore, the cyclicunimer is kept from being thoroughly extracted by a water treatment orthe like, and this is advantageous in view of fabric processing.

The cyclic unimer improves slipperiness of the polyamide yarn andmaintains the flexibility of the fabric. When the proportion of thecyclic unimer component in the polyamide compound is 0.1% or more, evenafter passing through a high-temperature environment, the fabric isallowed to maintain good retention of its tear tenacity by the slowbleed out of the cyclic unimer component. Similarly, the fabric afterpassing through a high-temperature environment is prevented fromincrease of friction and keeps good slipperiness. Furthermore, thefabric successfully keeps the flexibility without becoming coarse andhard due to plasticization effect. Accordingly, the fabric after thermalaging does not become coarse and hard but maintains the airtightnesswithout promoting gas leakage through the seam and at the same time,causes no reduction in the deployment rate of the airbag.

When the proportion of the cyclic unimer in the amide compound is 3.0%or less, the fabric after passing through a high-temperature environmentis kept from excessive reduction in the sliding resistance anddeterioration of the pressure resistance as an airbag.

As for the cyclic unimer, it is preferred to appropriately add thecyclic unimer during spinning into a polyamide fiber. An oligomerobtained as a sublimation material powder from a polyamide 6•6 moltenpolymer is purified by recrystallization, whereby an oligomer comprisinga cyclic unimer as the main component can be obtained.

Also, the cyclic unimer is finely dispersed by the fatty acid metal saltand thereby contributes to enhancement of mechanical properties of thepolyamide fiber. This effect of the cyclic unimer is not inhibited bythe zinc, aluminum and magnesium elements but rather exerts the effectin combination with such an aliphatic metal salt.

The proportion of the cyclic unimer component in the amide compound isdetermined by dissolving the fabric in an NMR solvent and performing a13C-NMR spectral analysis. For example, in the case of a polyamide 6•6polymer, the spectral analysis fundamentally followed the Davis proposal(R. D. Davis, et al., Macromolecules 2000, 33, 7088-7092). The carbon atthe β-position with respect to the amide nitrogen bonding site of thehexamethylenediamine skeleton in the polyamide 6•6 polymer exhibitsthree kinds of chemical shifts, that is, (1) carbon in a cyclic unimer,(2) carbon in the trans conformation in a chain polyamide and carbon ina cyclic polyamide except for a cyclic unimer, and (3) carbon in the cisconformation in a chain polyamide. The NMR peak intensity of (1) isdetermined by percentage (%) based on the total of peak intensities of(2) and (3) and taken as the proportion of the cyclic unimer in thepolyamide compound. In the case where the spectrum of the finish oilcomponent of the fiber is overlapped in the NMR spectrum, the spectrummay be analyzed by comparison after removing the finish oil component ofthe yarn by extraction with an organic solvent.

In the polyamide fabric of the present invention, the content of thefinish oil component is preferably from 0.01 to 2.0 wt %, morepreferably from 0.05 to 1.5 wt %, still more preferably from 0.1 to 0.7wt %. The finish oil component as used herein is a component extractedfrom the fabric with an organic solvent hexane, and the content thereofis the percentage of the weight of the extract based on the weight ofthe polyamide fabric. When the content of the finish oil component is0.01 wt % or more, tear tenacity of the fabric base cloth can bemaintained and enhanced. In particular, the surfactant component in thefinish oil component assists in bleeding out the cyclic unimer of thepolyamide yarn, appropriately promotes slip of yarn with each other dueto integration of the cyclic unimer and the finish oil component on thepolyamide yarn surface and contributes to maintaining and enhancing thetear tenacity after passing through a high-temperature environment. Thatis, as the airbag fabric, the gas pressure resistance during deploymentcan be expected to increase and therefore, the surfactant componentcontributes to burst prevention during deployment. The surfactantcomponent also greatly suppresses the increase of fabric friction andtherefore, contributes also to inhibiting delay of the deployment time.With only the finish oil component, the effect of maintaining andenhancing the tear tenacity in a high-temperature environment isgradually lost. However, due to the integration with the cyclic unimer,the effect is more successfully maintained.

When the content of the finish oil component is 2.0 wt % or less, theairbag fabric is not rejected in the burning property test (FMVSS302).

The finish oil component may be a remaining component derived from theprocess finish oil applied in the fiber production step and the weavingprocess step.

Other than those described above, within the range not impairing theeffects of the present invention, the original yarn may contain variousadditives usually used for improving the productivity or characteristicsin the production step or processing step of the original yarn. Forexample, a thermal stabilizer, an antioxidant, a light stabilizer, alubricating agent, an antistatic agent, a plasticizer, a thickener, apigment and a flame retardant may be incorporated.

In the fabric of the present invention, the polyamide yarn may be woveninto a fabric by a waterjet loom, an airjet loom, a rapier loom, amultiphase weaving machine or the like. As for the fabric texture, afabric such as plain fabric, twill fabric, satin fabric, variation orcombined texture fabric thereof, and multiaxial fabric are used, andamong these, a plain fabric is preferred because of its excellentmechanical properties and thinness. A double woven fabric capable ofweaving a bag may be also used.

In the weaving, a finish oil component may be applied to a warp yarn orthe like for enhancing the gathering and bundling property. The finishoil component applied here may be finally contained in the airbagfabric.

Subsequently, scouring and washing may be performed to remove excessivefinish oil component or contamination. In the scouring step, alkaliwashing or surfactant washing is performed in a warm water bath, but inthe present invention, cares must be taken not to remove zinc, aluminumand magnesium elements and furthermore, the cyclic unimer and the like.Rather, the fabric is preferably finished into an airbag fabric withoutperforming the scouring. More preferably, a fabric having an appropriateamount of the finish oil component after mostly eliminating the finishoil component by a waterjet loom is finished into an airbag fabricwithout passing through scouring. This facilitates control of the amountof contents necessary for the present invention and is profitable. Awarping finish oil or a finish oil of the weaving step, where alubricating agent and an antistatic agent are the main component, ispreferably contained in the final fabric.

In the scouring step, for decreasing the thermal stress at 120° C. ofthe weaving yarn constituting the fabric, the scouring is preferablyperformed by raising the scouring temperature. On the other hand, forkeeping high the thermal stress at 230° C. of the weaving yarnconstituting the fabric, it is preferred to select an appropriatescouring temperature or not perform the scouring. The conditions may beappropriately selected according to the property, particularly theshrinkage percentage, of the weaving yarn original yarn.

The fabric can be then finished into an airbag fabric through drying andheatsetting. In the drying and heatsetting of the fabric, with respectto each of the fabric width and feeding in the warp direction, theshrinkage amount and tension are preferably controlled. For example, atenter is used. For keeping high the thermal stress at 230° C. of theweaving yarn constituting the fabric, it is preferred to select the heattreatment temperature and process the fabric by a heat treatment whileapplying a tension without leaving the fabric to shrink. After the heattreatment, the fabric is preferably cooled rapidly while applying atension. In the case of using a low shrinkage yarn as the weaving yarn,non-setting is also preferred so as to maintain the thermal stress at230° C.

For reducing the weight of the airbag, the airbag fabric of the presentinvention is preferably used for the airbag with substantially nocoating of a resin or an elastomer. The fabric may be finally applied toa calendering process, but since reduction in the tear tenacity must notbe incurred, the fabric may be preferably used without applying acalendering process.

The airbag fabric of the present invention is cut and sewn and then maybe appropriately used for a driver's seat airbag, a passenger seatairbag, a backseat airbag, a side airbag, a knee airbag, an airbagbetween car seats, a side curtain airbag, a rear window curtain airbag,a pedestrian protection airbag and the like. In the airbag, thereinforcing cloth used for an inflator fixing port, a vent hole portionand the like or the member regulating the deployment shape of bag may bethe same fabric as the airbag fabric. Also, in sewing the airbag, onesheet of the airbag fabric piece formed by punching, fusion(heat-cutting) or cutting (cloth-cutting) or a plurality of such sheetsare used, and the peripheral edges thereof are sewn, whereby an airbagcan be formed. Furthermore, an airbag where the sewing of the peripheraledges is composed of single or double seam sewing may be also formed.

The fabric of the present invention can be used as an airbag by weavingit as a bag fabric and cutting the outer periphery of the binding part.

The airbag module of the present invention is preferably an airbagmodule obtained by combining the above-described airbag and an inflatorusing an explosive or a propellant.

EXAMPLES

The present invention is described in greater detail below by referringto Example and Comparative Examples, but the present invention is notlimited only to these Examples.

In Examples, the characteristic evaluation and the like of the airbagfabric were performed by the following methods.

(1) Basis Weight of Fabric:

Measurement was performed using a sample of 10 cm×10 cm in accordancewith JIS L1096, Appendix 3.

(2) Total Yarn Fineness of Raveled Yarn:

Warp and weft yarn raveled from the fabric were measured by setting thesample length to 25 cm in accordance with JIS L1096, Appendix 14.

(3) Tensile Characteristics of Raveled Yarn:

The yarns were inserted twists at 20 wists/25 cm, and a tensile test wasperformed with a chuck distance of 25 cm at a stretching speed of 30cm/min in accordance with JIS L1013 8.5.1. As for the specificload-elongation (%) of the raveled yarn, the elongation under a load of4.0 cN/dtex was read. Also, as for the initial tensile modulus, thestress (cN/dtex) per total yarn fineness at an elongation of 2.5% wasread.

(4) Number of Filaments of Raveled Yarn:

The number of constituent filaments was counted on the cross-sectionalphotograph of the fabric.

(5) Thermal Stress of Raveled Yarn:

Measurement was performed using CORD RHEOTESTER manufactured by ToyoSeiki Seisaku-Sho, Ltd. As for the temperature rise profile, the initialload was 0.02 cN/dtex, the sample length was 25 cm, and the temperaturerise was set such that in the EXP. mode, the initial temperature was 20°C. and the achieving temperature of 250° C. was achieved in 3 minutes.That is, the temperature rise rate was about 80° C./min. The stress wasdetermined at the point of 120° C. and 230° C.

(6) Entanglements of Raveled Yarn:

Entanglements was observed by letting the raveled yarns float on thesurface of fresh water.

(7) Number of Twists of Raveled Yarn:

The number of twists of the raveled yarn was measured with a chuck widthof 20 cm by using a twist counter in accordance with JIS L1096, Appendix13 and converted into the number of twists per m.

(8) Shrinkage in Boiling Water of Raveled Yarn:

The shrinkage in boiling water of the raveled yarn having a length of 25cm was measured in accordance with JIS L1013 8.18.1 (Method B).

(9) Cover Factor (CF):

This was determined according to the following formula:CF=(Dw)^(1/2) ×Tw+(Df)^(1/2) ×Tf  (1)(wherein Dw is the total yarn fineness (dtex) of the raveled yarn in thewarp direction, Df the total yarn fineness (dtex) of the raveled yarn inthe weft direction, Tw is the weave density (yarns/2.54 cm) of the warpyarn, and Tf is the weave density (yarns/2.54 cm) of the weft yarn).(10) Air Permeability by FRAZIER Method:

This was measured by JIS L 1096 8.27.1 Method A.

(11) Air Permeability Under High Pressure:

The air permeability under 200 kPa was determined by drawing awet-up/dry-up air permeation curve from an air pressure of 0 to an airpressure of 200 kPa with the immersion solution GalWick by usingCapillary Flow Porometer CFP-1200AEX (manufactured by Porous Metrials,Inc.).

(12) Tensile Strength and Elongation of Fabric:

The measurement was performed in accordance with JIS L1096 8.12.1 MethodA (strip method). As for the specific load-elongation (%) of the fabric,in the obtained stress-strain curve, the stress was converted into astress per one raveled yarn based on the weave density and the finenessof raveled yarn, and the elongation under a load corresponding to 4.0cN/dtex was determined.

(13) Weave Density:

The measurement was performed in accordance with JIS L1096, Appendix11A. A densimeter was used.

(14) Measurement of Fabric Surface:

A surface photograph was taken by SEM, and the dimension of the maximumwidth of the flared weaving yarn was measured. The average value of atleast 20 or more measurement points was determined and out of front andback surfaces, the larger value was employed as the maximum width W (mm)of the weaving yarn.

(15) DSC of Fabric:

The fabric sample was punched into a round shape of 6 mmφ that is almostthe same as the bottom size of the pan for DSC measurement, weighed, layon the bottom of the measurement pan, and swaged to the cover of thepan. The melting peak was observed at a temperature rise rate of 20°C./min. An endothermic peak appears in a shoulder shape before thecrystal melting peak near 260° C., and the temperature at which the peakrises from the base line was taken as the melting initiationtemperature. The area of the entire endothermic peak combining thecrystal melting peak and the shoulder part, from the base line was takenas the heat of melting (J/g). DSC7 manufactured by PERKIN-ELMER wasused.

(16) Quantitative Analysis of Metal:

The fabric sample in an amount of about 0.2 g was sampled in a Teflon(registered trademark)-made closed digestion vessel, and 5 ml ofhigh-purity nitric acid of analysis grade was added. Under the digestionpressure of 200° C.×20 minutes it was performed by a microwave digestionapparatus (ETHOS TC manufactured by Milestone General K.K.), and it wasconfirmed that the sample was completely digested and turned into acolorless and transparent solution. The volume was fixed to 50 ml withultrapure water to obtain a quantitative analysis solution, and thequantitative determination was performed by an internal standard methodusing an ICP mass analyzer (X Series X7 ICP-MS manufactured by ThermoFisher Scientific K.K.). The quantitative detection limit of copper andmagnesium elements was 0.03 ppm, and the quantitative detection limit ofeach of iron, zinc and aluminum elements was 0.01 ppm.

(17) Quantitative Analysis of Iodine:

As the pretreatment, about 50 mg of the fabric sample was burned in aflask enclosing oxygen, and iodine in the sample was absorbed by 20 mLof an aqueous 0.01 N sodium hydroxide solution. This solution is used asthe test solution for measurement. In the quantitative analysismeasurement, the quantity was determined from the calibration curve ofiodine by an internal standard method with indium (In) by using an ICPmass analyzer, X Series X7 ICP-MS, manufactured by Thermo FisherScientific K.K. The quantitative detection limit value was 0.5 ppm.

As for the quantitative determination of bromine, the quantity can bedetermined, for example, by using an ion chromatographic apparatus,2000i/sp, manufactured by Nippon Dionex K.K. The quantitative detectionlimit value is 20 ppm. In all of Examples, the quantity was below thedetection limit.

(18) Finish Oil Component of Fabric:

The fabric sample in an amount of 10 g was subjected to Soxhletextraction with 300 ml of n-hexane for 8 hours. From the dry weight ofthe n-hexane extract, the amount (wt %) of the finish oil component inthe sample was determined.

(19) Cyclic Unimer:

The fabric was dissolved in an NMR solvent and measured by ¹³C-NMR. Thesolution was completely dissolved and measured without adjusting the pH.The ¹³C-NMR spectrum was measured using an NMR apparatus, AVANCE(II)Model 400, manufactured by BRUKER under the following conditions.

NMR Conditions:

-   -   Sample concentration: 100 mg/0.8 ml-NMR solvent    -   NMR Solvent: hexafluoroisopropanol-d2    -   Measurement temperature: 25° C.    -   Pulse repetition interval: 2 seconds    -   Cumulated number: 18,000 times    -   Chemical shift basis: The peak of branching center, which        becomes the peak top of methine carbon of        hexafluoroisopropanol-d2, was set to 71.28 ppm. With respect to        the obtained polyamide 6•6 and the cyclic unimer contained, the        peak assignment of carbon (C2) located in β-position from        nitrogen-bonded site is shown in Table 1.

TABLE 1 Chemical Shift Calculation Assignment (ppm) Range (ppm) Chaincarbon: 2 30.5 0.4 Chain carbon: 2cis 31.5 0.2 Cyclic unimer carbon: C229.1 0.2

As for the cyclic unimer component ratio (A), the percentage wascalculated according to the following formula (2) from the peakintensities I each obtained by integrating the peaks in the calculationrange:A={I(C2)/(I(2)+I(2cis))}×100  (2)(20) Production of Airbag:

The airbag described in International Publication No. 99/28164, pamphletwas sewn. However, for the outer peripheral sewing, a two-rowdouble-thread chain stitch with a sewing thread of 235 dtex/2×3 and astitch number of 5.0 stitches/cm was employed. A vent hole was notprovided. The obtained airbag was inserted a retainer and subjected toairbag folding described in International Publication No. 01/9416,pamphlet, and an inflator was fixed. Subsequently, while not collapsingthe shape of the folded airbag, an loop cloth, which was obtained bysewing the same 3 cm-wide fabric as the airbag with a basting yarn intoan loop shape, was put entirely around the folded airbag and theinflator by arranging the basting portion to face the front.

(21) Deployment of Inflator:

An inflator of a pyro type having a 28.3 L tank pressure of 210 kPa asan output was used. The airbag was secured to inflator with retainer,and the pressure inside the airbag was observed from the retainer boltportion, and how the inflator is deployed was also observed using ahigh-speed video. The maximum deployment pressure near the maximumdiameter of deployment by inflator ignition was read as the inflatordeployment pressure (kPa). Also, the assembled airbag was treated at120° C. for 1,000 hours and thereafter, the maximum deployment pressurenear the maximum diameter of deployment by inflator ignition was readand taken as the inflator deployment pressure (kPa) after thermal aging.

(22) Close Proximity Deployment:

A baffle plate was provided at the position of 10 cm in front of theairbag, and how the inflator is deployed was observed using a high-speedvideo. The ruptured state after deployment was also checked, and theairbag ruptured upon production of a melted hole was judged as fusionrupture. Also, after treating the assembled airbag at 120° C. for 1,000hours, similarly, a baffle plate was provided, how the inflator isdeployed was observed using a high-speed video, and the bag afterdeployment was observed.

(23) Heat Resistance of Deployment Characteristics (Ratio of DeploymentTime Between Before and after Heat Treatment):

The airbag described in International Publication No. 99/28164,pamphlet, was sewn. However, for the outer peripheral sewing, a two-rowdouble-thread chain stitch with a sewing thread, both the upper threadand lower thread, of 235 dtex/2×3 and a stitch number of 5.0 stitches/cmwas employed. An inflator with a tank pressure of 200 kPa was mounted,and a deployment test was performed at ordinary temperature. The timeuntil the front deployment area reached 98% of the maximum deploymentarea in the high-speed VTR observation was taken as the deployment time.The ratio (%) of change in the deployment time between before and aftera treatment at 140° C. for 500 hours was determined.

(24) Heat Resistance of Dimensional Stability (Heat-ResistantDimensional Stability):

The outer peripheral size of the bag sewn above was compared betweenbefore and after a treatment at 140° C. for 500 hours, and the bagundergoing a change of 5% or more was judged as rejected.

(25) Deployment Characteristics Under Cold Conditions (Ratio ofDeployment Time Under Cold Conditions):

The airbag module was treated at 140° C. for 500 hours, then placed in atank at −35° C. overnight and thereafter, deployed by quickly connectingan ignition device, and the ratio (%) of change from the deployment timeat ordinary temperature before the heat treatment was determined.

(26) Fabric Burning Test:

Measurement was performed in accordance with FMVSS302. The sample wherethe burning rate was 102 mm/min or less was judged as passed.Furthermore, when the burning time was 60 seconds or less or the burnedlength was 51 mm or less, the sample was evaluated as passing theself-extinguishing property, i.e., self-extinguishing flame resistance.

Example 1

Sodium hypophosphite as a polymerization catalyst was added to anaqueous solution containing a neutralized salt of hexamethylenediamineand adipic acid, and condensation polymerization was performed in acontinuous polymerization apparatus. Subsequently, an aqueous solutionof copper iodide/potassium iodide as the thermal stabilizer was addedand after passing through post polymerization, a resin chip was formed.Thereafter, a polyamide 6•6 resin having a relative viscosity ηr of 3.1was obtained by solid phase polymerization. The iron element content ofthis polyamide 6•6 resin was 0.12 ppm. At the time of melt-spinning thepolyamide 6•6 resin by a melt extruder, cyclic unimer and aluminummontanate were added. For the filter of the melt-spinning machine, ametal nonwoven filter (average pore size: 15 microns) composed ofHastelloy C22 was used. Furthermore, the thread discharged was appliedwith a spin finish oil component and thermally drawn to obtain apolyamide 6•6 fiber. For the spin finish oil, a composition containing60 parts by weight of dioleyl thiodipropionate, 20 parts by weight ofhydrogenated castor oil EOA (molecular weight: 2,000) stearate and 20parts by weight of higher alcohol EOPO adduct (molecular weight: 1,500)was used. The number of entanglements was 7/m.

The thus-obtained filament yarn having a fineness of 470 dtex, afilament number of 72 and a single filament fineness of 6.5 dtex wasneither twisted nor sized and used to obtain a plain fabric in awaterjet room. Subsequently, without scouring, the fabric was dried byhot air at 80° C. and heatset by subjecting the fabric to heating at180° C. for 1 minute with an overfeed of 2% for both warp and weftdirections by the use of a pin tenter and then to quenching. An airbagfabric where both the weave density of warp yarn and the weave densityof weft yarn are 55 yarns/2.54 cm was obtained.

The total yarn fineness of the multi filament yarn (raveled yarn)constituting this airbag fabric, and the tensile tenacity, elongation atbreak, weave density, air permeability and amount of finish oilcomponent of the fabric are shown in Table 2. Similarly, the amounts ofcyclic unimer, copper element, halogen element (iodine), iron element,magnesium element, aluminum element and zinc element contained in theairbag fabric are shown in Table 2.

An airbag was sewn from the airbag fabric and after fixing an inflator,evaluated for the inflator deployment pressure. Also, the airbag wasexposed to 120° C. for 1,000 hours and evaluated for the inflatordeployment pressure after thermal aging. Furthermore, the presence orabsence of a rupture by a hot particle in the close proximity deploymentwas evaluated by observing the deployment. The results obtained are alsoshown in Table 2.

The inflator deployment pressure was sufficient without no loss of thedeployment gas and the inflator deployment pressure after thermal agingwas on the same level and sufficient. A rupture by a hot particle due toan inflator residue was not generated.

Example 2

The production and evaluation were performed in the same manner as inExample 1, except that a polyamide 6•6 fiber having a shrinkage inboiling water of 4.0% was used for the weaving yarn and neither scouringnor setting were performed after the weaving. The results are shown inTable 2. The inflator deployment pressure was sufficient without loss ofthe deployment gas and the inflator deployment pressure after thermalaging was on the same level and sufficient. A rupture by a hot particlewas not generated.

Example 3

The production and evaluation were performed in the same manner as inExample 1, except that a polyamide 6•6 fiber having a fineness of 350dtex, a filament number of 72, a single filament fineness of 4.9 dtexand a shrinkage in boiling water of 8.5% was used for the weaving yarnand after the weaving, the fabric was dried by hot air at 80° C.,subsequently heated by a heat roll at 160° C. with an overfeed of 3% infeeding the fabric and then quenched. The results are shown in Table 2.The inflator deployment pressure was sufficient without loss of thedeployment gas and the inflator deployment pressure after thermal agingwas on the same level and sufficient. A rupture by a hot particle wasnot generated.

Example 4

The production and evaluation were performed in the same manner as inExample 3, except that a polyamide 6•6 fiber having a fineness of 350dtex, a filament number of 144 and a single filament fineness of 2.4dtex was used for the weaving yarn. The results are shown in Table 2.The inflator deployment pressure was sufficient without loss of thedeployment gas and the inflator deployment pressure after thermal agingwas on the same level and sufficient. A rupture by a hot particle wasnot generated.

Example 5

The production and evaluation were performed in the same manner as inExample 2, except for using a multi filament yarn which was spun withoutadding a cyclic unimer. The gas utilization efficiency was good, butafter thermal aging for a long time, the maximum deployment pressurewhen deploying the airbag by a pyro-type inflator was slightly lower. Arupture by a hot particle was not generated.

Example 6

The production and evaluation were performed in the same manner as inExample 2, except that a metal nonwoven filter composed of SUS316L wasused for the polymer filtration at the spinning and aluminum montanatewas not added. The gas utilization efficiency was good, and a rupture bya hot particle was not generated. Under high-load conditions ofperforming close proximity deployment of the airbag after thermal agingfor a long time, the fiber near the seam was partially broken but arupture was not generated.

Example 7

The production and evaluation were performed in the same manner as inExample 1, except that a polyamide 6•6 fiber having a shrinkage inboiling water of 10.0% was used for the weaving yarn and after theweaving, at the heatsetting, the fabric without passing through scouringwas heated at 120° C. for 1 minute with an overfeed of 0% for both warpand weft directions by the use of a pin tenter and then quenched. Theresults are shown in Table 2. The inflator deployment pressure wassufficient without loss of the deployment gas, but after thermal aging,sewing wrinkles were outstanding and the inflator deployment pressurewas low. A rupture by a hot particle was not generated.

Comparative Example 1

The production and evaluation were performed in the same manner as inExample 1, except that after the weaving, the fabric was scoured in ascouring bath at 80° C. and in the subsequent heatsetting, heatset bysubjecting the fabric to heating at 210° C. for 1 minute with anoverfeed of 5% for both warp and weft directions by the use of a pintenter and then to slow cooling. The results are shown in Table 2. Theeffect of thermal stress during deployment was insufficient, loss of thedeployment gas occurred, the inflator deployment pressure was low, andthe inflator deployment pressure after thermal aging was also low. Arupture by a hot particle was not generated.

Comparative Example 2

The production and evaluation were performed in the same manner as inExample 1, except that a polyamide 6•6 fiber to which 35 entanglements/mwere imparted was used for the weaving yarn. The results are shown inTable 2. The weaving yarn coverage for the fabric surface was bad andthe air permeability under high pressure was high. Accordingly, loss ofthe deployment gas occurred, the inflator deployment pressure was low,and the inflator deployment pressure after thermal aging was also low. Arupture by a hot particle was not generated.

Comparative Example 3

The production and evaluation were performed in the same manner as inExample 1, except that a polyamide 6•6 fiber twisted at a frequency of100 twists/m was used for the weaving yarn. The results are shown inTable 2. The weaving yarn coverage for the fabric surface was bad andthe air permeability under high pressure was high. Accordingly, loss ofthe deployment gas occurred, the inflator deployment pressure was low,and the inflator deployment pressure after thermal aging was also low. Arupture by a hot particle was not generated.

Comparative Example 4

The production and evaluation were performed in the same manner as inComparative Example 2, except that a polyamide 6•6 fiber having astrength of 6.5 cN/dtex was used and after the weaving, in theheatsetting, the fabric was heatset by subjecting it to heating at 160°C. for 1 minute with an overfeed of 5% for both warp and weft directionsby the use of a pin tenter and then to slow cooling. The results areshown in Table 2. The fabric was readily strained at the elongationunder load, loss of the deployment gas occurred due to opening underhigh load, the inflator deployment pressure was low, and the inflatordeployment pressure after thermal aging was also low. In the closeproximity deployment, a rupture by a hot particle was not generated, buta seam rupture was generated.

Comparative Example 5

A plain fabric was woven in a waterjet room without sizing by using anuntwisted weaving yarn which is a polyethylene terephthalate fiberhaving a fineness of 470 dtex/96f, a tensile strength of 7.0 cN/dtex, atensile elongation at break of 22%, a shrinkage in boiling water of 0.9%and 15 entanglements/m. Subsequently, the fabric was scoured in ascouring bath at 80° C. and in the subsequent heatsetting, heatset bytreating the fabric by a two-stage heat roll at 150° C. and 180° C. withan overfeed of 2% for warp feed and then quenching it. The evaluationsof airbag deployment and the results thereof are shown together in Table2. The initial rigidity of the raveled yarn by a tensile test was highand this is considered to contribute to reduction in the airpermeability by the FRAZIER method. However, the summed specificload-elongation was large, as a result, the air permeability under highpressure of 200 kPa was not reduced, the summed thermal stress at 230°C. was low, and the pyro-inflator deployment pressure was low. Also, thethermal stress at 120° C. was high, and the air permeability at theinflator deployment pressure after thermal aging could not be kept lowand was insufficient. Furthermore, a rupture by a hot particle wasgenerated in close proximity deployment. In this bag, a folding creaseclearly remained.

TABLE 2 Example 1 2 3 4 5 6 7 <Original Shrinkage in boiling % 6.0 4.08.5 8.5 4.0 4.0 10.0 yarn> water Number of entanglements/m 7 7 7 7 7 7 7entanglements Number of twists/m 0 0 0 0 0 0 0 twists Strength cN/dtex8.2 8.6 8.5 8.2 8.6 8.6 8.2 Elongation under % 12.0 12.5 11.5 11.5 12.512.5 11.0 load of 4.0 cN/dtex <Processing Scouring temperature ° C. nonenone none none none none none conditions> Setting machine pin — heatheat — — pin tenter roll roll tenter Setting temperature ° C. 180 — 160160 — — 120 Overfeed % (warp/weft) 2/2 — 3/— 3/— — — 0/0 Cooling methodquenching — quenching quenching — — quenching <Raveled Total yarn warp,dtex 502 470 385 383 470 470 488 yarn> fineness weft, dtex 486 470 375373 470 470 485 Number of warp, filaments 72 72 72 144 72 72 72filaments weft, filaments 72 72 72 144 72 72 72 Single warp, dtex 7.06.5 5.3 2.7 6.5 6.5 6.8 filament weft, dtex 6.7 6.5 5.2 2.6 6.5 6.5 6.7fineness Strength of warp, cN/dtex 7.8 8.3 8.0 7.7 8.3 8.3 7.1 raveledyarn weft, cN/dtex 7.3 8.4 6.9 7.9 8.4 8.4 7.6 Elongation at warp, %18.9 21.5 24.5 23.1 21.5 21.5 19.0 break weft, % 20.2 21.5 22.2 22.821.5 21.5 20.2 Initial warp, cN/dtex 0.32 0.40 0.51 0.54 0.40 0.40 0.33tensile weft, cN/dtex 0.70 0.62 0.60 0.68 0.62 0.62 0.65 modulus (stressat 2.5% elongation) Specific warp, % 15.5 13.5 17.6 16.9 13.5 13.5 15.5load-elongation weft, % 13.2 13.0 15.9 15.4 13.0 13.0 13.5 (elongationunder load of 4.0 cN/dtex) Shrinkage in warp, % 0.9 3.0 1.7 0.4 3.0 3.05.0 boiling water weft, % −1.8 3.0 −2.3 −2.3 3.0 3.0 6.5 Number of warp,0 0 0 0 0 0 0 entaglements entanglements/m weft, 0 0 0 0 0 0 0entanglements/m Number of twists/m 0 0 0 0 0 0 0 twists twists/m 0 0 0 00 0 0 Thermal warp, cN/dtex 0.03 0.10 0.03 0.03 0.10 0.10 0.20 stress(120° C.) weft, cN/dtex 0.02 0.10 0.08 0.09 0.10 0.10 0.20 Thermal warp,cN/dtex 0.18 0.25 0.17 0.19 0.25 0.25 0.50 stress (230° C.) weft,cN/dtex 0.25 0.25 0.21 0.20 0.25 0.25 0.52 total, cN/dtex 0.43 0.50 0.380.39 0.50 0.50 1.02 <Fabric Fabric density warp, 55.0 55.0 63.5 59.055.0 55.0 55.0 characteristics> yarns/inch weft, 55.0 55.0 61.0 59.055.0 55.0 55.0 yarns/inch Widening ratio R(w) warp, % 125 110 109 115110 110 114 Widening ratio R(f) weft, % 99 95 93 96 95 95 95 Totalwidening Ws % 25 5 3 12 5 5 9 Cover factor (CF) based on 2445 2385 24272294 2385 2385 2426 dtex Basis weight g/m² 219 217 193 179 217 217 219Melting initiation ° C. 250.5 252.1 249.8 249.9 252.1 252.1 251.0temperature by DSC Heat of melting by J/g 78 78 78 78 78 78 78 DSC Airpermeability cc/cm²/sec 0.2 0.2 0.2 0.1 0.2 0.2 0.2 by FRAZIER Airpermeability cc/cm²/sec 180 130 165 106 130 130 150 at 200 kPa Fabricwarp, N/cm 680 600 580 576 600 600 720 tenacity weft, N/cm 750 640 590589 640 640 725 Fabric warp, % 38.8 40.0 43.7 39.9 40.0 40.0 39.0elongation at weft, % 32.5 30.0 34.5 33.7 30.0 30.0 33.0 break Fabricwarp, % 29.3 27.0 32.8 30.2 27.0 27.0 31.2 specific load- weft, % 21.419.0 23.0 22.4 19.0 19.0 20.0 elongation (elongation under load of 4.0cN/dtex) Total of specific % 50.7 46.0 55.8 52.6 46.0 46.0 51.2load-elongation Amount of finish oil % 0.18 0.18 0.19 0.19 0.18 0.180.18 component of fabric Cyclic unimer NMR % 0.91 0.91 0.91 0.91 0.020.91 0.91 content Cu Content ppm 50 50 50 50 50 50 50 I Content ppm 15001500 1500 1500 1500 1500 1500 Fe Content ppm 1.2 1.2 1.2 1.2 1.2 25 1.2Al Content ppm 2.0 2.0 2.0 2.0 2.0 0.01 2.0 Inflator deployment kPa 5050 50 50 50 50 50 pressure Inflator deployment kPa 50 50 50 50 45 50 10pressure after thermal aging (120° C., 1000 Hr) Close proximity passedpassed passed passed passed passed passed deployment Close proximitypassed passed passed passed passed seam passed deployment after breakingthermal aging (120° C., 1000 Hr) Comparative Example 1 2 3 4 5 <OriginalShrinkage in boiling % 6.0 6.0 6.0 6.0 0.9 yarn> water Number ofentanglements/m 7 35 7 7 15 entanglements Number of twists/m 0 0 100 0 0twists Strength cN/dtex 8.2 8.2 8.2 6.5 7.0 Elongation under % 12.0 12.012.0 12.0 14.0 load of 4.0 cN/dtex <Processing Scouring temperature ° C.100 80 80 80 80 conditions> Setting machine pin pin pin pin heat tentertenter tenter tenter roll Setting temperature ° C. 210 160 160 160150/180 Overfeed % (warp/weft) 5/5 2/2 2/2 5/5 2/0 Cooling method slowquenching quenching slow quenching cooling cooling <Raveled Total yarnwarp, dtex 504 502 507 501 475 yarn> fineness weft, dtex 490 486 486 489473 Number of warp, filaments 72 72 72 72 96 filaments weft, filaments72 72 72 72 96 Single warp, dtex 7.0 7.0 7.0 7.0 4.9 filament weft, dtex6.8 6.7 6.7 6.8 4.9 fineness Strength of warp, cN/dtex 6.9 7.8 7.8 5.86.7 raveled yarn weft, cN/dtex 6.8 7.3 7.3 6.2 6.5 Elongation at warp, %19.2 18.9 18.9 26.0 20.0 break weft, % 20.5 20.2 20.2 27.0 21.0 Initialwarp, cN/dtex 0.31 0.31 0.31 0.31 1.06 tensile weft, cN/dtex 0.66 0.660.61 0.70 1.27 modulus (stress at 2.5% elongation) Specific warp, % 17.515.5 15.5 18.5 16.0 load-elongation weft, % 15.2 13.2 13.2 18.0 15.8(elongation under load of 4.0 cN/dtex) Shrinkage in warp, % 0.2 0.9 0.90.2 0.5 boiling water weft, % −2.5 −1.8 −1.8 −2.5 0.7 Number of warp, 025 0 0 0 entaglements entanglements/m weft, 0 25 0 0 0 entanglements/mNumber of twists/m 0 0 100 0 0 twists twists/m 0 0 0 0 0 Thermal warp,cN/dtex 0.01 0.01 0.01 0.01 0.01 stress (120° C.) weft, cN/dtex 0.020.02 0.02 0.02 0.01 Thermal warp, cN/dtex 0.13 0.14 0.14 0.13 0.12stress (230° C.) weft, cN/dtex 0.18 0.25 0.23 0.18 0.14 total, cN/dtex0.31 0.39 0.37 0.31 0.26 <Fabric Fabric density warp, 55.1 55.0 55.055.1 55.0 characteristics> yarns/inch weft, 55.1 55.0 55.0 55.1 55.0yarns/inch Widening ratio R(w) warp, % 126 100 95 125 125 Widening ratioR(f) weft, % 100 94 95 99 99 Total widening Ws % 26 −6 −10 26 26 Coverfactor (CF) based on 2457 2445 2451 2452 2395 dtex Basis weight g/m² 220219 219 219 217 Melting initiation ° C. 249.5 251.0 251.0 250.0 241.6temperature by DSC Heat of melting by J/g 78 78 78 78 53 DSC Airpermeability cc/cm²/sec 0.1 0.2 0.2 0.1 0.1 by FRAZIER Air permeabilitycc/cm²/sec 165 250 380 180 205 at 200 kPa Fabric warp, N/cm 720 606 606500 615 tenacity weft, N/cm 725 645 645 530 632 Fabric warp, % 39.0 40.040.0 50.0 42.0 elongation at weft, % 33.0 29.3 29.3 45.0 38.0 breakFabric warp, % 31.0 30.6 30.6 37.1 35.0 specific load- weft, % 24.0 20.320.3 30.0 25.0 elongation (elongation under load of 4.0 cN/dtex) Totalof specific % 55.0 51.0 51.0 67.1 60.0 load-elongation Amount of finishoil % 0.05 0.05 0.05 0.05 0.05 component of fabric Cyclic unimer NMR %0.30 0.62 0.62 0.62 — content Cu Content ppm 50 50 50 50 — I Content ppm1500 1500 1500 1500 — Fe Content ppm 1.2 1.2 1.2 1.2 5.0 Al Content ppm2.0 2.0 2.0 2.0 — Inflator deployment kPa 30 30 10 20 40 pressureInflator deployment kPa 30 40 20 20 40 pressure after thermal aging(120° C., 1000 Hr) Close proximity passed passed passed seam rupturedeployment rupture by hot particle Close proximity passed passed passed− +− deployment after thermal aging (120° C., 1000 Hr)

Examples 8 to 10

Airbag fabrics were obtained in the same manner as in Example 1, exceptfor changing the amount added of the cyclic unimer during spinning. Theairbags sewn were evaluated for the ratio of deployment time betweenbefore and after heat treatment, the heat resistance of dimensionalstability, the ratio of deployment time under cold conditions and thefabric burning test. The results are shown in Table 3.

The airbags of Examples 8 and 9 had mechanical characteristics necessaryfor an airbag and excellent tear tenacity retention after heat treatmentand were excellent in the air permeability retention ratio after heattreatment and the characteristics related to the airbag deploymentspeed, such as low frictional properties and flexibility. Particularly,in the deployment under cold conditions, the deployment speed wasreduced due to reduction in the generated gas pressure but wellmaintained. In Example 10, the frictional coefficient after heattreatment was high, the flexibility was poor and the airbag deploymentafter heat treatment and under cold conditions was slightly delayed, buta rupture of the bag was not caused.

TABLE 3 Example Example Example Example 8 Example 9 10 11 12 Ratio ofcyclic % 0.91 2.50 0.02 0.91 0.91 unimer component of fabric Oil contentof % 0.18 0.18 0.18 0.19 1.2 fabric Cu Element ppm 50 50 50 50 50 FeElement ppm 1.20 1.20 1.20 1.20 1.20 Al Element ppm 2.0 2.0 2.0 2.0 2.0Ratio of deployment 103 100 110 103 100 time between before and afterheat treatment Ratio of deployment 120 117 138 120 115 time under coldconditions Fabric burning test self- self- self- self- 75 mm/minextinguishing extinguishing extinguishing extinguishing Heat-resistantpassed passed passed passed passed dimensional stability

Example 11

Polymerization and spinning were performed in the same manner as inExample 4 to obtain a filament yarn composed of a drawn polyamide 6•6fiber yarn. Using this multi filament yarn, a plain fabric was obtainedin a waterjet room in the same manner as in Example 4. The obtainedfabric was dried and then heatset at 180° C. for 1 minute to obtain anairbag fabric. The results including the evaluations of the airbag areshown in Table 3.

Example 12

The same procedure as in Example 11 was performed except that a finishoil component having the same composition as the spinning finish oil wasimparted by immersion after the weaving and then the fabric was driedand heatset. Incidentally, the content of the finish oil component afterheatsetting was 1.2 wt %. The results are shown together in Table 2. Theburning test gave a rating of slight fire spread but was passed, and thedeployability of bag was very good.

INDUSTRIAL APPLICABILITY

The fabric of the present invention can be suitably used as abody-restraining airbag for absorbing impact on the human body in avehicle collision accident or the like. In particular, the fabric of thepresent invention is suitable as a lightweight compact airbag module.

The invention claimed is:
 1. An airbag fabric comprising a polyamideyarn, wherein the cyclic unimer content in the fabric is from 0.1 to3.0% based on all amide bond units, the air permeability of the fabricunder a pressure of 200 kPa is from 10 to 200 cc/cm²/sec and in thethermal stress of the constituent yarn as measured under the conditionsof an initial load of 0.02 cN/dtex, a yarn length of 25 cm and atemperature rise rate of 80° C./min, the summed thermal stress of thetotal of the warp yarn and the weft yarn at 230° C. is from 0.33 to 1.20cN/dtex.
 2. The airbag fabric according to claim 1, wherein thepolyamide fiber is obtained by melt-spinning with the addition of anoligomer containing a cyclic unimer.
 3. The airbag fabric according toclaim 1, wherein the content of the spin finish component in the fabricis from 0.01 to 2.0 wt %.
 4. The airbag fabric according to claim 1,wherein the total widening Ws as the sum of the widening ratio R(f) ofthe weft yarn and the widening ratio R(w) of the warp yarn on the fabricsurface is from 0 to 40%.
 5. The airbag fabric according to claim 1,wherein the widening ratio R(f) of the weft yarn on the fabric surfaceis from 90 to 120% and the widening ratio R(w) of the warp yarn on thefabric surface is from 105 to 135%.
 6. The airbag fabric according toclaim 1, wherein in the stress-strain curve of the fabric, the totalvalue of the elongation under a load corresponding to 4.0 cN/dtex interms of a stress per one yarn constituting the fabric in the warp yarndirection of the fabric and that in the weft yarn direction is from 40.0to 58.0%.
 7. The airbag fabric according to claim 1, wherein in DSCmeasurement of measuring the fabric at a temperature rise rate of 20°C./min, the melting initiation temperature is from 245 to 280° C. andthe heat of melting is from 60 to 100 J/g.
 8. The airbag fabricaccording to claim 1, wherein the thermal stress determined by measuringthe constituent yarn of the fabric under the conditions of an initialload of 0.02 cN/dtex, a yarn length of 25 cm and a temperature rise rateof 80° C./min is from 0.005 to 0.10 cN/dtex at 120° C. in both the warpyarn and the weft yarn.
 9. The airbag fabric according to claim 1,wherein the constituent yarn is a polyamide 6.6 yarn having a relativeviscosity of 2.7 to 4.7, a single filament fineness of 0.8 to 8.0 dtex,a total yarn fineness of 100 to 800 dtex, a tensile tenacity of 5.0 to11.0 cN/dtex, an elongation at break of 15 to 35% and a shrinkage inboiling water of −4.5 to 5.0%.
 10. The airbag fabric according to claim1, which is not coated with a resin or an elastomer.
 11. An airbag usingthe airbag fabric according to claim
 1. 12. An airbag module using theairbag according to claim 11.